Purpose This course discusses techniques for analyzing and eliminating noise in microcontroller (MCU) and microprocessor (MPU) based embedded systems. Objectives Learn about a method for performing a system-level EMI test. See how to evaluate current balance. Gain a basic knowledge of tests for measuring the emissions from LSI devices that can be used for product selection. Content 18 pages Learning Time 30 minutes Course Introduction

Reducing EMI EMI reduction is a goal shared by both the semiconductor experts who design MPUs and other LSI devices, and by the engineers who apply those chips in embedded systems ECU Electronic Control Unit EMI Electromagnetic Interference Explanation of Terms A microcontroller chip is composed of a core, I/O ports, and power supply circuitry. The core consists of the CPU, ROM, RAM, and blocks implementing timers, communication, and analog functions. Power supply Two power supplies are applied to the LSI: Vcc and Vss. The core power supply internal to the LSI is VCL (internal step-down). The Vss-based power supply routed through the LSI is VSL. Harness Cables (wires) connecting a board and power supply or connecting one unit in a system to another Balun LISN TEM Cell WBFC Core A room designed to block radiation from the outside and to minimize reflections off the room’s walls, ceiling, and floor A passive electronic device that converts between balanced and unbalanced electrical signals CISPR 25 International Special Committee on Radio Interference (CISPR) publication 25: “Limits and methods of measuring radio disturbance characteristics for the protection of receivers on board vehicles.” CISPR is a sub-committee of the International Electrotechnical Commission (IEC). Line Impedance Stabilization Network Transverse Electromagnetic Cell Workbench Faraday Cage Anechoic chamber

System-level evaluation - Example: performed on three test boards - Test method for measuring emissions from wiring harness: (CISPR 25 equivalent) Radiation levels ranged from high for board A to low for board C Radiation from Wiring Harness Test setup LISN Antenna Circuit board with MPU Harness Anechoic chamber Board B Board C Board A

Near-field distribution was measured also, using an EMV-200 test system - A sensor coil on a probe rotates and moves with precision in three dimensions to scan and record the EMI radiated from the circuit board Data from the CISPR 25 test and the EMV-200 scan was used to examine the correspondence between the field strength and system level evaluation at the connector position EMI from Circuit Board EMV-200 Probe with sensor coil Data from near-field scan MPU Power supply connector Circuit board f = 80MHz

Emission Measurement Results With probe above the harness connector, there is a direct relationship between the antenna and near-field probe readings - Using a low-emissions MCU reduces emissions at the wiring harness connector on the board Moving from a 2-layer board to a 4-layer board further reduces emissions at the wiring harness connector Harness mounting area MCU Board MHz Harness mounting area MCU Board Harness mounting area MCU Board A Directly above MCU Above harness mounting area

Evaluating Current Balance in PCB -Test board provides extra pads to which 470Ω resistors can be connected to divert current through loops on left and right, creating differences between the signal and return currents in the area highlighted by the pink oval -Near-field scan data of the entire board was obtained for three test cases: Case 1: No resistors were connected, so currents in measurement area were balanced Case 2: a 470Ω resistor was connected on left side of board, creating a 10% current unbalance in the measurement area Case 3: Two 470Ω resistors were connected on the left and right sides of the board, creating a 20% unbalance in the measurement area Near-field measurements show the common- mode radiation caused by unbalanced currents flowing in the circuit board Left loopRight loop Line width = 1.3mm Termination (50  ) Pads 100, 90 or 80% 100% Area in which a difference between the signal current and return current can be created

h = 2.5mm f = 80MHz Case 1: Current Balanced With no 470Ω resistors connected, current was balanced, so minimum levels of EMI were detected when the EMV-200’s probe scanned the measurement area of the printed circuit board Case A 100% No 470Ω resistors (Both loops open)

Case 2: Current Unbalanced by 10% With a 470Ω resistor connected, a 10% current unbalance was created, which caused the EMI to grow to moderate levels in the area of the unbalance Case B Case A h = 2.5mm f = 80MHz 100% 90% Additional resistor (470  ) 1/10

Case 3: Current Unbalanced by 20% With both 470Ω resistors connected, a 20% current unbalance created; this caused the EMI to becomes high in the area of the unbalance Case B Case C Case A h = 2.5mm f = 80MHz 100% 90% 100% 80% Two additional resistors (470  ) 1/10 Near-field scans can help locate the cause of EMI problems

Board Layout Affects Emissions Terminated Microstrip line Reference Microstrip Line Signal input: 100MHz sine wave, 1.0Vp-p ) An ideal microstrip line shows a fairly uniform current distribution and minimum emissions Pitch: 5mm; Scan height: 10mm Scanned from bottom side (reference

Layout Affects Emissions — 2 Symmetric Pattern Emissions increase as the width of the pc board becomes more narrow Pitch: 5mm; Scan height: 10mm Scanned from bottom side (reference

Layout Affects Emissions — 3 Asymmetric Pattern The asymmetric pc board causes even more emissions Pitch: 5mm; Scan height: 10mm Scanned from bottom side (reference

Emission Measurement Standards The international standards listed here are used to measure electromagnetic emissions* from MCUs and other ICs Standard No.: Title Latest Standard Document Issue DateRemarks IEC : General conditions and definitions IS[IEC ] IEC : Measurement of radiated emissions, TEM-cell and wideband TEM-cell Method IS[IEC ] TS[IEC TS ] IS [IEC ] IS[IEC ] IEC : Measurement of radiated emissions, Surface Scan Method (Technical Specifications) IEC : Measurement of conducted emissions, 1-ohm/50-ohm Direct Coupling Method [IEC Ed. 1.1] Edition IS [IEC ] IEC : Measurement of conducted emissions, Workbench Faraday Cage Method IEC : Measurement of conducted emissions, Magnetic Probe Method IS: IEC International Standard TS: Technical Specification *Measurement range: 150kHz to 1GHz

IC Vcc 49Ω 1Ω 50Ω in IC Vcc 50Ω in IC Vcc 950Ω 50Ω 1K Ohm ex. vn IS Supply Current Measurement The VDE probe and magnetic probe methods are international standards; the resistor-divider probe method is not VDE ProbeMagnetic ProbeResistor-Divider Probe [IEC TS ][IEC ]

IS EM Radiation, CM Voltage Testing These three methods are also good for emissions testing; the Faraday Cage method can measure common-mode voltage for each part of the circuit board Faraday CageLoop Probe u Vcc vnvn [IEC ][IEC TS ] TS 50Ω TEM Cell [IEC ] IS

Problem with Normal TEM Cell When measuring emissions from LSI devices, the combined EM field data are almost identical to that of the magnetic field measurement alone; the electric field data is difficult to see Magnetic field Electric field + Magnetic field (combined result produced by a normal TEM cell measurement) TEM cell output level (dB) Frequency (MHz) TEM cell method (normal) TerminatorMeasuring system 50Ω TEM Cell Electric field

Electric field coupling (50Ω terminator) 50Ω terminator (magnetic field coupling) Output Renesas “Hybrid Balun” Applying the TEM Cell Method With the “hybrid balun” that Renesas has adopted, voltages proportional to a pure electric field and a pure magnetic field can be obtained Photo shows an electric field coupling Changing the terminator and output port results in a magnetic field coupling

 System-level evaluation techniques  Importance of circuit board layout  Methods for evaluating emissions from LSI devices Course Summary For more information on specific devices and related support products and material, please visit our Web site: